The applicant has developed a series of lightweight, compact self-propelled lawn aeration machines characterized by upper and lower wheel sets rotatably mounted in journals fixed to a machine frame riser, and to opposite sides thereof for rotation of the dual wheels for the upper sets and dual wheels for the lower sets about a horizontal axis. The wheels are linked by jack shafts for synchronized rotation, with a given upper and lower wheel of each wheel set being linked by a jack shaft for synchronized rotation or by a chain coupled to the wheels, which wheels take the form of sprocket wheels, and wherein the upper wheel of each wheel set pivotably mounts one end of a crank arm, while the other end of the crank arm reciprocates through a bushing rotatably mounted on the lower wheel of the wheel set. Further, in each case, whether the wheel sets are coupled by a jack shaft or a crank arm, the lower, terminal end of the respective jack shaft or crank arm fixedly mounts an in-line tine functioning to penetrate the turf. The tines are hollow and the tine penetration results in the creation of a cylindrical plug of turf and earth, which plug is retracted from the ground during retraction of the tine, thus producing small diameter, relatively short depth air holes within the turf.
Further, applicant's machines are exemplified by provision of means at respective wheels for pivotably coupling the jack shaft or crank arm to the upper and lower wheels at circumferentially offset positions with respect to coaxial wheels adjacent thereto for the adjacent tines and/or at selective radially different positions with respect to the axis of rotation of the wheels to vary the forward travel speed of the machine or to vary the timing in terms of penetration and retraction of the tines borne by the machine. As may be appreciated, it is the penetration and subsequent retraction of the machine that causes the machine to self-drive, that is to move itself forwardly over the surface of the turf while penetrating the turf, and in most machines, carving out a small diameter cylindrical plug which is removed during retraction of the tine. The machines developed by the applicant are exemplified by U.S. Pat. Nos. 4,606,411; 4,606,412; and 4,662,456. In the machines as exemplified by these three patents, the lower wheels of each of the wheel sets may function as high speed flywheels to provide more than adequate force for penetrating the hollow tines into the turf and retraction therefrom in time sequence, even when the turf is relatively dry and hard. Further, in U.S. Pat. No. 4,606,412, the upper wheel of each wheel set determines the depth of penetration of the tine borne by a crank arm emanating from the upper wheel, while the radial position of a bushing on the lower wheel of each wheel set determines the extent of travel of the machine over the turf as a result of tine penetration and removal.
While the self-propelled lawn aeration machines of my prior patents are highly effective, are light weight and may operate at relatively high speed, and while they function adequately to self-drive the machine across the surface of the turf by tine penetration and removal, they are somewhat complicated by the necessity of employing upper and lower wheels forming a series of wheel sets, with the wheels mounted for rotation about their axes on the frame supporting the tine driving mechanism. The machines as set forth in the patents cited above are in turn an improvement over an art which is developed over the years and which art is exemplified by a large number of patents cited in column 1 of my '456 Patent. Reference may be had thereto for a further understanding and appreciation of the type of mechanism to which the present invention constitutes a further improvement.
In somewhat more recent years, a turf aerating machine has been developed in which a generally vertically reciprocating crank arm is rotatably supported at its upper end to a crankshaft, and is guided near its lower end by a horizontal plate with a longitudinal horizontal elongated slot for laterally guiding the lower end of the crank arm, such that a tine, fixed to the lower end of the crank arm, penetrates the turf during rotation of the crank arm. This causes the machine to be self-driven forwardly during that rotation, and during which the tine sidewardly penetrates the earth and is retracted therefrom. Such machine is exemplified by U.S. Pat. No. 4,658,909. In U.S. Pat. No. 4,658,909, a flat horizontal plate underlying the crankshaft is slotted fore and aft at laterally spaced positions, through which slots project the crank arms bearing the fixedly mounted tines, such that the crank arms are guided by the slots during rotation of the crankshaft and during projection of the tines into the turf and retraction therefrom effecting self-drive of the machine. A tension coil spring fixed at one end to the frame and its opposite end to a crank arm bearing the tine, causes each crank arm to be biased towards the forward end of the slot when the tine is engaged in the ground due to the forward motion of the aerator over the turf. When the tine is retracted from the ground by the crankshaft, the crank arm is returned to the forward end of the slot by the coil spring as a result of the stored energy due to expansion of the spring. While tending to return the tine arms to a forwardmost position prior to tine repenetration into the turf, such action is too slow for high speed operation of the machine, the biasing force may vary from spring to spring, and the springs are subject to breakage. Additionally, the springs are too slow in reacting, thus incapable of repositioning the tine arm at high cyclic speeds to which the more recent lawn aerating machines are subjected.
It is therefore a primary object of this invention to provide an improved lawn aeration machine which utilizes a single series of axially aligned light weight metal discs fixedly mounted to a common shaft segments and commonly driven, which employ tine arms pivotably mounted to the wheel at circumferentially offset position, where the tine arms are guided by projecting through slots formed by a chassis member above the projecting lower end of the tine arms to which the tines are fixedly mounted, in which the fore and aft oscillation of the tine arm is positively controlled and synchronized, which eliminates the needs for return springs, which is devoid of any hydraulics, which eliminates the possibility of oil damage to the turf, in which the tines work in a straight up and down reciprocation to eliminate turf sidewall compaction and which permits easier maintenance of the machine.